1. Field of the Invention
The present invention relates to a pattern transferring method used in lithography for semiconductor IC circuits, and more particularly, it relates to a method for transferring patterns formed on a mask onto a beam-sensitive substrate by illumination with a charged particle beam such as an electron beam or an ion beam.
2. Description of the Related Art
In recent years, exposure apparatuses using a charged particle beam to achieve both high resolving power of exposure and high throughput have been developed. Among such exposure apparatuses, in the past, exposure apparatuses of the collective transfer type in which patterns for one die (corresponding to one of a plurality of integrated circuits formed on a single wafer) or a plurality of dies are transferred from a mask to a beam-sensitive substrate totally or collectively (in a lump) have been developed. However, in these collective transfer type exposure apparatuses, it was difficult to manufacture the mask acting as a negative and to limit aberration of an optical system below a predetermined value within a large optical field corresponding to one or more dies. In consideration of the above, exposure apparatuses of a separate transfer type have recently been considered in which a pattern to be transferred to a wafer is divided into a plurality of small regions smaller than an area corresponding to one die and then these small regions are successively transferred onto the wafer to complete the entire pattern.
In such exposure apparatuses of separate transfer type, the small regions formed on the mask are separated from each other by opaque border zones. Since such opaque zones should not be formed on the beam-sensitive substrate (wafer), a charged particle beam passing through a given small region is deflected by a deflector so that a pattern image corresponding to current region is formed on the wafer directly adjacent to the previously formed pattern image.
In the above-mentioned arrangement, since an amount of deflection is increased as the small region is spaced apart from a center of the mask, optical fields available to the mask and/or the beam-sensitive substrate are limited.